01 - Whisk together mayonnaise, ketchup, yellow mustard, sweet pickle relish, white vinegar, smoked paprika, and black pepper in a small bowl until smooth. Set aside to allow flavors to meld.
02 - Place a large skillet or griddle over medium-high heat and allow it to become thoroughly hot.
03 - Divide ground beef into 8 equal portions and roll into balls. Season generously with kosher salt and freshly ground black pepper on all sides.
04 - Place beef balls onto the hot skillet. Press each ball firmly with a heavy spatula to smash into thin, wide patties. Cook undisturbed for 2-3 minutes until the edges are crispy and deeply browned. Flip and cook 1-2 minutes longer. Transfer to a paper towel-lined plate.
05 - Distribute mixed salad greens evenly among four serving bowls. Arrange cherry tomatoes, red onion, dill pickles, avocado slices, and shredded cheddar cheese over the greens.
06 - Place the crispy smashed burger patties on top of each bowl, distributing evenly among servings.
07 - Drizzle with prepared smash sauce and sprinkle with crispy fried onions if desired. Serve immediately while patties are still warm.